Light-sensitive layers for the printing industry



Patented Aug. 31, 1954 LIGHT-SENSITIVE LAYERS FOR THE PRINTING INDUSTRY Wilhelm Neugebauer, Wiesbaden-Biebrich, Germany, assignor, by mesne assignments, to Azoplate Corporation, Summit, N. J., a corporation of New Jersey No Drawing.

Application May 10, 1950,

Serial No. 161,260

Claims priority, application Germany May 14, 1949 Claims.

The present invention relates to the production of light-sensitive materials suitable for use in the graphic industry. More particularly, it relates to the preparation of lithographic light-sensitive layers by means of a polymerization product chosen from the group consisting of polyacrylic acid amide, the polymerized homologues of acrylic amide, polymeric acrylic acid amides substituted at the N-atom and copolymers in which the before-mentioned substances are contained.

In lithography metal plates or stone plates or otherwise used bases or supports are provided with a layer consisting of colloidal substances of various kinds, which are subject to an alteration of their properties, particularly of their solubility when struck by light rays in the presence of lightsensitive substances, such as salts of chromic acid. For producing a colloid layer on the support according to prior art methods some natural products, such as gum arabic, fish glue, gelatin and albumin, are used. These substances have the draw-back of being somewhat variable in their properties and consequently yield lithographic printing materials showing certain variations in use. Moreover, the present colloids are readily attacked by microorganisms.

It has already been proposed to use synthetic colloid substances for producing a lithographic printing layer, the number of the compounds coming into consideration for practical use being very small. Polyvinylalcohol has been used to a certain extent for these purposes; it is hardened under the influence of light, if salts or chromic acid or certain diazo compounds, such as have been described in U. S. Patent 2,063,631, are contained in the polyvinylalcohol.

Experiments have been made aiming to cause the hardening of the polyvinylalcohol by means of azido compounds. This would be interesting, because layers which have been produced on metallic surfaces and do contain azido compounds can be stored without being subject to any alteration. The matter is complicated, however, because rather big quantities of the azido compounds must be added to the polyvinylalcohol in order to obtain a hardening effect on exposure to light. If the same quantities of azido compounds are used together with polyvinylalcohol, which quantities are suflicient to produce a hardening effect when the other known light sensitive substances capable of hardening colloids are involved, then the desired hardening effect is not attained. Likewise gum arabic and fish glue are not satisfactorily hardened, if they are exposed to light after azido compounds have been added, as has been described in French Patent 886,716.

It has been found that polymeric amides of acrylic acid can be used with good success for producing lithographic light-sensitive layers. Using polymerized acrylic acid amides according to the present invention carries the outstanding advantage of an always uniform quality of the light-sensitive layers thus produced, this uniformity being due to the synthetic nature of the product which can be prepared without any difficulty in a standard quality.

Derivatives of the polyacrylic acid amide in which one or both hydrogen atoms of the NHzgroup are substituted, e. g., by alkyl groups, can also be used in the same manner, furthermore interpolymers containing acrylic acid amides and other vinyl compounds, such as vinyl acetate may be used. The same holds true with respect to the polymerization products of the homologues of the acrylic acid amides, such as polymethacrylic acid amide.

Mixtures of the polyacrylic acid amides and their above mentioned equivalents with other soluble colloid substances can be used with a similar good effect. Products having a high viscosity are particularly suitable for the formation'of lithographic printing layers.

The hardening of the polyacrylic acid amide layers under the action of light can be brought about by adding as light-sensitive substances chromates, diazo compounds or azides. Layers containing azides are of particular importance for the above-mentioned reason: namely, they are very stable when coated onto zinc or aluminum plates and their ability of producing good copies is retained for a long time. With these materials it is possible to market pre-sensitized lithographic plates which relieve the plate maker from the necessity of coating the printing plates shortly before use.

Other auxiliary substances usual in the art, such as agents increasing the sensitivity to light of the layers, hardening agents and so on may also be incorporated into the layer.

Most of the layer forming substances of the present invention are soluble in water. In consequence thereof the light-sensitive layer is very easy to produce. The light-sensitive substance is added to an aqueous solution of the polyacrylic acid amide compound and this solution is then applied in known manner to the support and subsequently dried. On account of the layers being soluble in water they can also be developed in a very simple manner after having been exposed to bases or supports for the layers. foils of plastics, glass, paper, textile fabrics and light under an original. In case the substances necessary for the formation of the layer are insoluble water, mixtures of alcoholand water or only alcohol are used.

The production of copying patterns and stencils as well as of printing plates for gravure, planographic and ofiset printing and furthermore for application in intaglio printing are within the scope of the invention.

The methods of producing the polymeric acrylic acid amides and thier substitution products suitable for practicing the present invention are well known. Some of them have been published in the French Patent No. 898,577 andin the Journal of the American Chemical Society 69 (1947), p. 1911-1914.

In order to illustrate the present invention without any intention of limiting the scope thereof, the following examples are inserted:

(1) An aqueous solution containing of a highly .viscous polymerization product of N- dimethylacry1ic acid amide and 0.5% of a diazo compound formed by condensing in 80% sulfuric acid 1 mol of p-diazo-diphenylamine-sulfate and 1 mol of formaldehyde is applied to an aluminum foil or thin aluminum plate in the usual manner, e. g. by means of a plate-whirler, and is then dried at a moderately raised temperature. The light sensitized metal foil is exposed under a negative and rinsed with water so that the portions of the light-sensitive layer which were not struck by light are dissolved and washed away. The colloid substance as far as it is hardened is dyed by means of a diluted aqueous solution of methylene blue (Schultz, Farbstoiftabellen, 7. ed., volume I,

p. 449) a positive blue imagebeing obtained.

Instead of an aluminium foil or thin aluminium plate other metal foils or plates can be used as For example,

soon may be used. The images obtained may be used as opaque surface images or as transparent images as well as copying masters. If so desired the solutions used for producing the light-sensitive layer can contain dyestuffs, sensitizing or stabilizing substances and the like.

Other derivatives of the polyacrylic acid amide substituted at the N-atom, e. g., the polymerization product of N-monomethyl-acrylic acid amide, can also be used instead of the polymeric N-dimethyl-acrylic acid amide described above.

(2) The mode of proceeding is the same as had been described in Example 1, with the exception, that the exposure takes place under a positive. The exposed foil after having been washed with water is dried andthe negative colloidal'image is developed to become a positive printing plate ready for use. The further processing of the plate is carried out in known manner by first etching and then coating the negative with a thin layer of lacquer, using an alcoholic lacquer solution, followed by rubbing over the plate with a greasy printing ink and subsequently removing the original patternalso sometimes referred to as the resist which does not participate in the printing process.

(3) A zinc plate is coated in the usual manner with an aqueous solution containing 5% of a poly-N-diethyl-acrylic acid amide having a K- value of 70 and 0.5% of ammonium bichromate. The plate when dry is exposed to light under a positive, the unhardened parts are dissolved by a rinse of cold water and the plate is processed according to the details given in Example 2, to a positive printing plate in known manner.

(4) A foil consisting of an interpolymer of vinyl chloride and vinyl acetate is coated in known manner on one side with a 5% aqueous solution of polyacrylic acid amide having a K- value of 80, the solution containing in addition 0.5% of the sodium salt of 4,4'-diazidostilbene- 2,2-disulfom'c acid. The coated foil is exposed under a negative pattern, washed out with cold water, dyed at normal temperature with a 4% aqueous solution of sirius light blue G (Schultz, Farbstofftabellen, 7. ed., addition volume I (1934), p. 131) Result: a tanned blue positive image.

(5) "0.5 part of the sodium salt of 4,4'-diazidostilbene-2,2-disulfonic acid and 0.5 part of eosin are dissolved in 100 parts of a solution containing 5% of a copolymer produced of parts of acrylic acid amide and 20 parts of vinyl acetate. The solvents used for preparing the solution of the copolymer are alcohol (1 part) and water (4 parts). The solution thus obtained is applied by means of a plate-whirler to an aluminium plate having a surface anodically oxidized. The plate, after being dried, is exposed to light under a positive pattern and is developed by means of water, the colloidal layer being removed at those places which have not been struck by light. After drying, the plate is coated with an alcoholic lacquer and subsequently rubbed over with a greasy ink. All parts of the colloid layer which have been hardened under the influence of the light and which are sometimes referred to as the stencil, are then removed by means of water and with the aid of a brush. A positive printing plate suitable for use in flatand offset-printing is obtained. If desired, the printing plate can be etched in known manner before the lacquer is applied. The etching may be effected by means of a concentrated solution of iron chloride.

(6) 09 part of the sodium salt of 4,4'-diazidostilbene-2,2-disulfonic acid is dissolved in parts of an aqueous solution containing 5% of polyacrylic acid amide and 4% of polyvinyl alcohol. This solution is applied to an aluminium plate by means of a plate-whirler. The plate, after being dried, is exposed to light under a. positive pattern, subsequently dyed with a 4% aqueous solution of sirius light blue G (Schultz, Farbstofftabellen, 7. ed., addition volume I (1934), p. 131) and developed by a rinse of cold water the colloidal layerbeing removed at those places which have not been struck by light. After drying, the plate is coated with an alcoholic lacquer and then rubbed over with a greasy ink. All parts of the colloid layer which have been hardened under the influence of the light are then removed by means of water and with the aid of a brush. A positive printing plate suitable for use in flatand offset-printing is obtained. v

(7) 0.6 part of the sodium salt of 4,4'-diazidostilbene-2,2-disulfonic acid is dissolved in 100 parts of an aqueous-alcoholic solution (1:1) containing 3% of polymeric N-dimethyl-acrylic acid amide and 3% of polyvinylpyrrolidone. This solution is applied to an aluminium plate by means of a plate-whirler. After drying, the coated plate is exposed to light under a positive pattern, dyed with a 4% solution of sirius light blue G (Schultz, Farbstofftabellen, 7. ed., addition volume I (1934), p. 131) and subsequently developed by a rinse of water. All parts of the colloidal layer which have not been struck by light are washed out. The plate, after being dried, is then coated with a lacquer consisting of a 14% solution of a phenolic resin in a 1:1

mixture of ethyl acetate and benzene and rubbed over with a greasy ink as soon as the lacquer has become dry. Now all parts of the colloid layer which have been hardened under the influence of the light are removed by means of water using a brush. A positive printing plate suit able for use in flat and offset-printing is obtained.

After having disclosed and described in all details my present invention What I claim is:

1. Light sensitive material suitable for use in the manufacture of printing plates comprising a base and a light sensitive layer thereon, said layer including a polyacrylamide in which both hydrogen atoms of the Nl-iz group are substituted by alkyl radicals and an aside compound which is an alkali salt of 4,4-diazidostilbene--2,2 disulfonic acid.

2. The material of claim 1 in which the alkyl radicals are ethyl groups.

3. The material of claim 1 in which the alkyl radicals are methyl groups.

4. The material of claim 1 in which the azido compound is the sodium salt of 4,4-diazidostilbene-2,2' disulfonic acid.

5. Material for use in photomechanical reproduction comprising a solution of an azide compound which is an alkali salt of 4A'-diazidosti1bene-2,2' disulionic acid in a polyacrylamide in which both hydrogen atoms of the NH2 group are substituted by alkyl radicals, saidsolution being light-sensitive.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,587,269 Beebe et a1 June 1, 1926 1,628,279 Schmidt et a1 May 10, 1927 1,845,989 Schmidt et a1 Feb. 16, 1932 2,184,288 Dangelmajer Dec. 26', 1939 2,461,023 Barnes Feb. 8, 1949 2,522,771 Barnes Sept. 19, 1950 FOREIGN PATENTS Number Country Date 886,716 France July 12, 1943 232,1 i5 Switzerland Aug. 1, 1944 

1. LIGHT SENSITIVE MATERIAL SUITABLE FOR USE IN THE MANUFACTURE OF PRINTING PLATES COMPRSING A BASE AND A LIGHT SENSITIVE LAYER THEREON, SAID LAYER INCLUDING A POLYACRYLAMIDE IN WHICH BOTH HYDROGEN ATOMS OF THE NH2 GROUP ARE SUBSTITUTE BY ALKYL RADICALS AND AN AZIDO COMPOUND WHICH IS AN ALKALI SALT OF 4,4''-DIAZIDOSTIBENE-2,2'' DISULFONIC ACID. 